Method and apparatus for regenerative heating in thermal power plants

ABSTRACT

A method and apparatus is herein provided for power plants which improves the useful life thereof by increasing their operating efficiency above that heretofore obtained, and at the same time achieving a substantial decrease in operating costs. This results from elimination of the numerous conventional high pressure extraction sources for feedwater heating and the utilization of a vapor compressor to compress relatively low-pressure extraction vapor to a pressure equal to, and preferably greater than, that obtained from the previously employed plurality of cascaded high pressure extraction points. Such compressed high-pressure and high-temperature vapor is then supplied to the vapor-liquid cycle for regeneration.

United States Patent Teg tmeyer [76] Inventor: Edward K.'Tegtmeyer, 33

Grandview FL, North Caldwell, NJ. 07006 Feb. 25, 1971 Appl. No.: 118,621

[22] Filed:

US. Cl. 60/678 Int Cl Folk 7/38 stantial decrease in operating costs. This results from [58] Fieid 67 89 elimination of the numerous conventional high pressure extraction sources for feedwater heating and the utilization of a vapor compressor to compress rela- 1 tively low-pressure extraction vapor to a pressure [56] References cued equal to, and preferably greater than, that' obtained UNITED STATES PATENTS from the previously employed plurality of cascaded 9l3,330 2/ I903 Wadagaki 60/92 high pressure extraction points. Such compressed 1,066,348 I913 f= 60/92 high-pressure and high-temperature vapor is then supl,563,690 12/1925 Crrstlanl 60/92 plied to the vap0r ]iquid Cycle for regeneration 2,939,286 6/1960 Pavlecka 60/92 X 3,175,953 3/1965 Nettel et al. 60/67 UX 10 Claims, 1 Drawing Figure esfiifia GENERATOR CONDENSER 2'" STAGE STEAM COMPRESSOR 1451 Oct. 22, 1974 Primary Examiner-Edgar W. Geoghegan Assistant ExaminerAllen M. Ostrager Attorney, Agent, or Firm-Pennie & Edmonds [5 7] ABSTRACT A method and apparatus is herein provided for power plants which improves the useful life thereof by increasing their operating efficiency above that heretofore obtained, and at the same time achieving a sub- 1" spas; s rew 39 cot/113 a o 22 -4- I COOLING WATER L P /5 attests t HE HEATER HTR 30 HTR COBlI ISZNPSATE 26 BOILER FEED DRAIN PUMP 3/1971 Harris 60/65 METHOD AND APPARATUS FOR REGENERATIVE HEATING llN THERMAL POWER PLANTS BACKGROUND OF THE INVENTION Conventional power plants consist of a steam generator, using either fossil-fuel or nuclear fuel, that supplies steam to a multi-stage turbine-generator exhausting to a condenser at high vacuum. The condensate therefrom is pumped through a number of feedwater heaters that utilize steam extracted from progressively higher pressure stages of the turbine, until the final feedwater temperature is increased as high as possible consistent with design of the steam generator, or economic considerations of the cycle. The foregoing, commonly referred to as regenerative feedwater heating, results in a high cycle efficiency being primarily dependent upon the number of extraction points and feedwater heaters that it is economically feasible to utilize.

There are, however, inherent basic limitations to the conventional regererative feedwater heating cycle. It is well recognized that the available thermodynamic gain progressively diminishes with each additional feedwater heater that is added to the cycle. This is because of the fact that as the turbine extraction point moves closer to turbine throttle pressure, the steam passes through a smaller portion of the turbine resulting in less work, before it is extracted and condensed in the feedwater heater. It is therefore obvious that if turbine throttle pressure were used for this purpose there would be no thermodynamic gain whatsoever and there exists an economic point, dependent on fuel costs, at which the capital costs of additional feedwater heaters in the cycle would become greater than the thermodynamic gain achieved over the expected useful life of the power plant.

SUMMARY OF THE PRESENT INVENTION It is'accordingly the primary object of the present invention to increase the cycle efficiency of power plants to a much greater degree than heretofore thermodynamically possible in a conventional regenerative cycle regardless of the number of feedwater heaters that can be economically utilized in such power plants.

Another object of the present invention is the provision of a power plant wherein a plurality of the higher pressure conventional extraction feedwater heaters are eliminated from the turbine cycle as well as all associated high pressure turbine extraction sources.

. Another object of the present invention is the provision of a high efficiency power plant wherein a high pressure feedwater heater is provided which is supplied with vapor at suitable pressure-temperature conditions from a vapor compressor to achieve the desired final feedwater temperature.

Another object of the present invention is the provision of a high efficiency power plant wherein a compressor is utilized to supply suitable high pressure and high temperature vapor to a feedwater heater and wherein the low pressure vapor supplied to said compressor is extracted from the power-plant turbines after the greatest part of the available work energy of such vapor has been utilized to produce work within the turbines.

Still further objects of the present invention will become obvious to those skilled in the art by reference to the accompanying drawing wherein:

The single FIGURE is a diagrammatic illustration of a power plant in accordance with the present invention, wherein a compressor is employed to compress relatively low pressure extraction vapor from the turbine after its greatest work energy has been utilized in such turbine, thereby eliminating the conventional high pressure turbineextraction sources for feedwater heating that decreases the work availability of such vapor within the turbine.

Referring now to the drawing, in detail, which shows a typical embodiment that the present invention may take, a vapor generator 5 is diagrammatically shown in the FIGURE wherein vapor, such as steam, is produced and supplied to a turbine throttle valve 6 at a high pressure and high temperature. From the throttle valve 6 such steam expands through a high pressure turbine 7. Since this turbine 7 is devoid of the former conventional high pressure extraction sources A and B for feedwater heating, the steam that otherwise would have been extracted now performs additional work within such turbine before exhausting and passing to a reheater 8 located within the steam generator 5 wherev such steam is reheated again to a high temperature. l

This reheated steam then flows through an intercept valve 9, where its expanded flow passes through tandem connected intermediate pressure turbine 10, also devoid of former conventional, high pressure extraction sources C and D for feedwater heating which again produces the aforementioned increased work performance, and then flows'through a tandem connected low pressure turbine 12 from which it exhausts to a condenser 13 at a high vacuum. The work energy resulting from the expanding steam passing through the tandem turbine sections 7, 10 and 12, drives an electric generator 14 coupled to these turbines, resulting in conversion of the energy into electrical power at high efficiency.

The vapor-liquid, or feedwater, regenerative cycle is performed by apparatus comprising a condensate pump 15 which removes the condensate feedwater from the condenser 13 and pumps it through low pressure heaters 16 and 17 into a deaerating feedwater heater 18, with such heaters receiving extraction steam pressure from points of the low pressure turbine 12 through lines 19 and 20, respectively. Since the deaerating feedwater heater 18 is also connected by a line 22 to the low pressure turbine 12, the condensatefeedwater is accordingly heated to the saturation temperature corresponding to the extraction steam pressure from another point of the low pressure turbine 12. This heated condensate-feedwater is removed from the deaerating feedwater heater 18 by a boiler feed pump 23 and forced through a high pressure heater 24 to the steam generator 5, at a sufficiently high discharge pressure to overcome piping, heat exchanger and boiler internal resistances. The high pressure heater 24 is sup plied with steam from a steam compressor 25 also connected to the low-pressure turbine 12 by a line 26, which thus imparts to the steam supplied to the steam generator 5 a pressure and saturation temperature equal to or greater than that normally heretofore supplied from the highest pressure extraction source of a steam turbine.

For example, the steam compressor 25 receives steam from the low pressure turbine 12 at approximately 15 p.s.i.a. and compresses it to about 900 p'.s.i.a. corresponding to a saturation temperature of 532F which, neglecting superheat in the compressed steam, would result in heating the feedwater flowing through high pressure heater 24, to this saturation temperature of about 532F when supplied to the steam generator 5. The steam compressor 25 may alternatively be equipped with an intercooler 31 and/or an aftercooler 32. Either the intercooler 31 or the aftercooler 32 or both receive cooling steam by line 33 through valve 38 or by line 35 through valve 37 which is in turn heated by exchange with the hotter compressed steam in the intercooler 31 or aftercooler 32 and subsequently recycled by line 34 through valve 39 or by line 36 through valve 40 to a point in the turbine cycle downstream of the point from which the cooler high pressure discharged steam was received, thus imparting additional useful heat to the intermediate pressure and/or low pressure turbines. Drains from the high pressure heater 24 flow through a drain line 27 to the deaerating feedwater heater 18, and similarly drains from low pressure heater l7 flow through a drain line 28 to low pressure heater 16, from which such drains are drawn by a drain pump 29 and returned to the feedwater system through a line 30. i

The foregoing feedwater regenerative cycle for the conversion of low pressure extraction steam to high pressure steam, by compression for feedwater heating as above described, inherently results in substantially greater total utilization of available energy within the turbine sections than when such steam is extracted at higher pressure turbine levels and then utilized for regenerative feedwater heating, as heretofore universally employed. Also, a further important result from the vapor-liquid, or feedwater, regenerative cycle of the present invention ensues from the fact that the increased utilization of energy, resulting from compressionregeneration as herein described, produces a net gain in cycle efficiency. This follows from the fact that all the work done by the compressor, except for neglible losses, is returned to the cycle in the enthalpy of vapor leaving the compressor and recovered in the vaporliquid cycle.

Moreover, the gain in additional work within the turbines, by elimination of the previously employed extraction, is substantially greater than the work required to compress the low pressure extraction steam to the same pressure-temperature levels that otherwise would be required by direct extraction to feedwater heaters at these same relatively high levels. At the same time, the net gain in cycle efficiency results in a corresponding reduction in atmospheric pollution from fossil-fuel plants.

The complexity of the power installation is also reduccd by the inherent initially high condensing temperature difference between the compressed vapor and the feedwater that permits substantially less feedwater heating surfaces than conventionally required and which heretofore necessitated a plurality of feedwater heaters. Consequently, the elimination of the plurality of conventional high pressure feedwater heaters more than offsets the costs of the compressor andits driver which at the same time simplifies the design and construction of the power plant.

it should accordingly be obvious to those skilled in the art that an improved method and apparatus for the preheating of feedwater or other liquids in thermal power plants has been herein shown and described. Moreover, it is to be understood that further modifications and refinements thereof may be made without departing from the spirit and scope of the present invention. For example, some amount of intercooling can be provided for the vapor compressor to reduce its power requirements, which intercooling could use low temperature vapor from the turbine cycle and returning to the turbine cycle, with some of the superheat of compression being recovered and supplied to the cycle as partial reheat of the vapor used, resulting in an additional thermodynamic gain.

Furthermore, the vapor compression principle of the present invention can be used advantageously for vapor reheating, especially in nuclear installations where vapor is supplied to the turbine throttle at saturated conditions and the moisture resulting from expansion of the vapor through moisture regions produces a reduction of turbine efficiency. Such vapor compression not only reduces losses due to moisture in the vapor but also can provide one or more stages of reheat, thus establishing a higher reheat gain factor than is economically possible with initial saturated vapor as presently utilized for conventional saturated vapor nuclear installations.

Having shown and described a preferred embodiment of my present invention, l claim:

1. The method of operating a vapor-liquid cycle power plant for the production of energy output at high efficiency comprising a turbine cycle of low and high pressureand a vapor generator comprising:

extracting vapor from a relatively low pressure source of the vapor-liquid cycle,

compressing such extracted vapor to produce a high pressure and a high temperature vapor,

and supplying such high pressure and high temperature vapor to the vapor-liquid cycle power plant by returning it to the vapor generator. 2. The method of operating a vapor-liquid cycle power plant for the production of energy output at high efficiency comprising a turbine cycle of low and high pressure and a vapor generator comprising:

producing vapor in a vapor generator, passing such vapor through a plurality of tandem turbines connected to an electric generator followed by condensation of such vapor to a liquid,

passing extracted vapor through a compressor to compress such extracted vapor to a high pressure and high temperature,

and supplying such high pressure and high temperature vapor to the vapor-liquid cycle of the power plant for regeneration.

3. The method of operating a power plant for the production of energy output at high efficiency as set forth in claim 2, wherein the compressor supplying the high pressure heater with high pressure and high temperature vapor is itself supplied with extraction vapor from the last tandem turbine.

4. The method of operating a power plant for the production of energy output at high efficiency comprising:

producing vapor in a vapor generator,

passing such vapor through a high pressure turbine and exhausting the vapor therefrom through the vapor generator for reheating and on to an intermediate pressure turbine,

passing the vapor unextracted through the intermediate pressure turbine and exhausting it therefrom through a low pressure turbine to a condenser with formation of a vapor-liquid condensate,

coupling a generator to the turbine shaft for generapumping the vapor-liquid condensate from the condenser and through a series of low pressure heaters and a deaerating feedwater heater,

heating the vapor-liquid condensate in the low pressure heater and the deaerating feedwater heater with extracted vapor from the low pressure turbine,

electrical energy comprising:

a vapor generator,

a high pressure turbine connected to said vapor generator for passing of the high pressure and temperature vapor therethrough to cause operation of said high pressure turbine andthe passage of the exhaust vapor therefrom back to said high pressure vapor generator for reheating,

tandem connected intermediate pressure turbine and a low pressure turbine, with said intermediate pressure turbine being connected to said vapor generator and operable upon the passage of high pressure vapor progressively through said tandem connected intermediate pressure and low pressure turbines, as well as through said high pressure turbine, to cause operation of an electrical generator;

condenser connected to said low pressure turbine for collecting the exhaust vapor condensate therein as a liquid supply,

a plurality of low pressure heaters and a deaerating feedwater heater connected to the condenser for receiving extraction vapor therefrom,

a high pressure heater connected to said deaerating' feedwater heater and to said vapor generator,

means operable to force the condensed vapor from said condenser and serially through said low pressure heaters, said deaerating feedwater heater, and said high pressure heater, to said vapor generator;

and a compressor operable to supply high pressure and high temperature vapor to said high pressure heater, to cause the liquid passing therethrough to be substantially raised in temperature and pressure when supplied to said vapor generator.

6. A high efficiency power plant for the generation of electrical energy as set forth in claim 5, wherein the compressor which supplies high pressure and high temperature vapor energy to said liquid is imparted thereto through said high pressure heater.

7. A high efficiency power plant for the generation of electrical energy as set forth in claim 5 wherein the compressor, which produces the high pressure and high temperature vapor supplied to the high pressure heater, receives low pressure exhaust vapor from said low pressure turbine. 1 v

8. The method of claim 5 wherein the vapor compressor is provided with one or more intercoolers between stages to reduce its power requirements.

9. The method of claim 5 wherein the vapor compressor is provided with an aftercooler.

vapors to the turbine cycle.-

" e STATES PATENT OFFICE CERTIFICATE .OF CORRECTION NO. 3,842,605 Dated Oct 22, 1914' Tnventcr(s) Edward K Tegtmeyer It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

1. Column 3, line 41 reads the vaporliquid" should read the vapor-liquid Signed and sealed this 14th day of January 1975.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer 7 Commissioner of Patents FORM PC4050 (IO-59) I 0.5. eovllmun 'r IRINTING oFrlcz Ian 0-3693". 

1. The method of operating a vapor-liquid cycle power plant for the production of energy output at high efficiency comprising a turbine cycle of low and high pressure and a vapor generator comprising: extracting vapor from a relatively low pressure source of the vapor-liquid cycle, compressing such extracted vapor to produce a high pressure and a high temperature vapor, and supplying such high pressure and high temperature vapor to the vapor-liquid cycle power plant by returning it to the vapor generator.
 2. The method of operating a vapor-liquid cycle power plant for the production of energy output at high efficiency comprising a turbine cycle of low and high pressure and a vapor generator comprising: producing vapor in a vapor generator, passing such vapor through a plurality of tandem turbines connected to an electric generator followed by condensation of such vapor to a liquid, passing extracted vapor through a compressor to compress such extracted vapor to a high pressure and high temperature, and supplying such high pressure and high temperature vapor to the vapor-liquid cycle of the power plant for regeneration.
 3. The method of operating a power plant for the production of energy output at high efficiency as set forth in claim 2, wherein the compressor supplying the high pressure heater with high pressure and high temperature vapor is itself supplied with extraction vapor from the last tandem turbine.
 4. The method of operating a power plant for the production of energy output at high efficiency comprising: producing vapor in a vapor generator, passing such vapor through a high pressure turbine and exhausting the vapor therefrom through the vapor generator for reheating and on to an intermediate pressure turbine, passing the vapor unextracted through the intermediate pressure turbine and exhausting it therefrom through a low pressure turbine to a condenser with formation of a vapor-liquid condensate, coupling a generator to the turbine shaft for generation of electrical energy by the expansion of the vapor in passing through the turbines, pumping the vapor-liquid condensate from the condenser and through a series of low pressure heaters and a deaerating feedwater heater, heating the vapor-liquid condensate in the low pressure heater and the deaerating feedwater heater with extracted vapor from the low pressure turbine, removing the heated liquid from the deaerating feedwater heater into a high pressure heater, and supplying the high pressure heater with high pressure vapor from a compressor to return the compressed vapor energy to the liquid as it is passed on to the vapor generator.
 5. A high efficiency power plant for the generation of electrical energy comprising: a vapor generator, a high pressure turbine connected to said vapor generator for passing of the high pressure and temperature vapor therethrough to cause operation of said high pressure turbine and the passage of the exhaust vapor therefrom back to said high pressure vapor generator for reheating, a tandem connected intermediate pressure turbine and a low pressure turbine, with said intermediate pressure turbine being connected to said vapor generator and operable upon the passage of high pressure vapor progressIvely through said tandem connected intermediate pressure and low pressure turbines, as well as through said high pressure turbine, to cause operation of an electrical generator; a condenser connected to said low pressure turbine for collecting the exhaust vapor condensate therein as a liquid supply, a plurality of low pressure heaters and a deaerating feedwater heater connected to the condenser for receiving extraction vapor therefrom, a high pressure heater connected to said deaerating feedwater heater and to said vapor generator, means operable to force the condensed vapor from said condenser and serially through said low pressure heaters, said deaerating feedwater heater, and said high pressure heater, to said vapor generator; and a compressor operable to supply high pressure and high temperature vapor to said high pressure heater, to cause the liquid passing therethrough to be substantially raised in temperature and pressure when supplied to said vapor generator.
 6. A high efficiency power plant for the generation of electrical energy as set forth in claim 5, wherein the compressor which supplies high pressure and high temperature vapor energy to said liquid is imparted thereto through said high pressure heater.
 7. A high efficiency power plant for the generation of electrical energy as set forth in claim 5, wherein the compressor, which produces the high pressure and high temperature vapor supplied to the high pressure heater, receives low pressure exhaust vapor from said low pressure turbine.
 8. The method of claim 5 wherein the vapor compressor is provided with one or more intercoolers between stages to reduce its power requirements.
 9. The method of claim 5 wherein the vapor compressor is provided with an aftercooler.
 10. The method of claims 8 or 9 wherein the intercoolers or aftercooler or both receive as a cooling medium low temperature vapor from the turbine cycle thereby effecting the recovery of most of the superheat of compression and returning these partially reheated vapors to the turbine cycle. 